Dual spray painting



Jan. 26, 1960 Filed Nov. 19, 1956 A. D. SLATKIN DUAL SPRAY PAINTING 2 Sheets-Sheet 1 FIG. 1

A.D. SLATKIN vINVENTOR.

ATTORNEYS K Jan. 26, 1960 A. D. SLATKIN 2,922,584

DUAL SPRAY PAINTING Filed Nov. 19, 1956 2 Sheets-Sheet 2 A. D. SLATKIN INVENTOR.

BY WM ATTORNEYS United States Patent DUAL SPRAY PAINTING Alfred D. Slatkin, Birmingham, Mich., assignor to Ford Motor Company, Dearborn, Mich., a corporation of Delaware Application November 19, 1956, Serial No. 622,997

2 Claims. (Cl. 239-245) This invention relates to an apparatus for the electro static transportation and selective deposition of finely atomized particles of liquid. It is particularly directed to the repetitious electrostatic painting of similar articles in which the paint is first atomized by centrifugal force. The atomized particles after having been given an electrical charge are then propelled to and deposited upon the article to be painted by electrostatic forces.

In recent years the painting art has resorted to the use of rotating sharp edged metallic cups or discs for the production of a charged mist or spray of paint. These metallic atomizers are rotated about their own axis and paint is fed to the central portion of the atomizer, whence it flows to the periphery under the influence of centrifugal force. At this periphery the paint is atomized electrostatically and departs from the atomizer in a direction which amounts to the vector sum of the centrifugal and electrostatic forces.

As a result of extensive experimentation with this type of apparatus it has been discovered that a so called doughnut effect is often produced especially when painting extended flat surfaces. This defect is manifested by a central zone which is painted to a lesser extent surrounded by a properly painted annulus.

An object of this invention is to eliminate this defect and enable a uniform coating to be applied to extended surfaces.

A further object of this invention is to substitute mechanical or centrifugal atomization for the electrostatic atomization of the prior art. .This enables the atomizing forces and transportation and deposition forces to be independently varied.

A further object of this invention is to provide an apparatus useful for the commercial application of the process involving only centrifugal atomization.

Figures 1 and 2 of the drawing have been supplied to aid in a ready understanding of the operation of this invention.

Figure 1 is an elevation view partially in section of the apparatus employed for the execution of this invention, and

Figure 2 is a sectional view of the end of the apparatus shown in Figure 1 which includes the rotating cups.

Figure 1 is a general elevation view of the spray painting apparatus employing a pair of concentric cups. In this view only outer cup is shown. The driving and paint supplying mechanisms for outer cup 10 and inner cup 11 are contained within housing 12 which is preferably constructed of metal. Housing 12 and associated cups 10 and 11 are charged to a high potential by voltage source 13 by means of conductor 14. Housing 12 is usually charged with a potential which is negative with respect to the ground but this is not necessary. The opposite polarity may be employed if desired.

Air motor 15 is supplied with compressed air through coupling 16 and serves to rotate inner cup 11 and outer cup 10. Paint is supplied to coupling 17 and couplings 18 and 19 serve to introduce compressed air employed 2,922,584 Patented Jan; 26, 1960 2 to interrupt and reestablish the flow of paint. Cap 20 is rounded and serves to reduce corona losses from this apparatus when working at high voltages.

Figure 2 is a detailed sectional drawing of inner cup 11 and outer cup 10 and the apparatus employed to rotate these cups and to supply them with paint. Air motor 15 (Figure 1) drives shaft 21 which supports gears 22 and 23. Gear 22 is larger than gear 23 and in turn propels driven gear 24 which is secured to hollow shaft 25 which is solidly connected to and rotates inner cup 11.

Similarly gear 23 meshes with driven gear 26 which is mounted upon hollow bushing 27, which supports and drives outer cup 10. In this manner a mechanism is provided for rotating inner cup 11 at a much higher speed than outer cup 10.

Paint flowing in through coupling 17 (Figure 1) is introduced into central conduit 28 and flows axially along this conduit and emerges through opening 29 into the interior of inner cup 11 and through opening 30 into the interior of outer cup 10. These openings may be located so that they project paint on to the interior of the cups at any desired axial location.

The structure of cups 10 and 11, shown in the solid lines, represents a fairly sharp edge. However, it has been found from experience that the edge of the cups 10 and 11 may be rounded to any desired extent to diminish the effects of corona discharge Without adversely affecting the centrifugal atomizing action of these cups. This rounded edge structure is shown in the dotted lines.

It is essential that the inner and outer cup rotate sufficiently rapidly to enable the paint to be atomized solely by centrifugal action. A rotating speed of 3000 revolutions a minute has been found satisfactory for a 6 inch outer cup with a conventional priming coat. The inner cup rotates between 2 and 3 times faster than the outer cup. The rotational speed should be varied to accommodate such variables as paint viscosity, composition and temperature. The high voltage on the cups and steep electrostatic gradient immediately adjacent the cups electrically charge the atomized particles of paint and permit their acceleration, transportation and deposition by the electrostatic field existing between the cups and the object to be painted.

Extensive use has been made of this 'type of painting apparatus and it has been found to successfully avoid the occurrence of objectionable doughnut defect.

I claim as my invention:

1. In an electrostatic paint applying apparatus, a housing, an atomizing head on said housing comprising a pair of coaxial cups, concentric shaft means within said housing rotatably supporting said cups, drive means coupled to said shaft means and constructed and arranged to rotate the inner cup at a higher speed than the outer cup, and conduit means extending through the inner of said concentric shaft means, said conduit means having a first discharge port opening into the inner cup and a second discharge port opening into the outer cup whereby paint is supplied to the inner surface of each of said cups from the common conduit means, both cups being rotated at a speed sutlicient to atomize the paint solely by centrifugal action.

2. In an electrostatic paint applying apparatus, a housing, an atomizing head on said housing comprising a pair of coaxial cups, concentric shaft means within said housing rotatably supporting said cups, drive means coupled to said shaft means and constructed and arranged to rotate the inner cup at a higher speed than the outer cup, and conduit means extending through the inner of said concentric shaft means, said conduit means having a first discharge port opening into the inner cup 3, i '4 and a second discharge port'opcning into the outer cup References Cited in the file of this patent whereby paint is supplied to the innersurface of each of said cups from the common conduit means, both cups UNITED STATES PATENTS being rotated at a speed sufficient to atomize the paint 2,473,035 Melde June 1949 solely by centrifugal action, the'atomizing edge of, each 5 2,764,712 Iuvman Sept 251 1956 2,809,902 Ransburg Oct. 15, 1957 cup being roundedio diminish corona effect. 

